The general field of this invention is the focusing of light. More specifically, this invention involves locating the focal point of planar parallel light passing through a converging lens, whether from a laser or a classic source, in an automatic way.
More specifically, this invention involves focusing a laser beam in an automated process or device for the manufacture of integrated circuit chips and wafers. This can be used for various purposes including exact positioning and leveling of the surface of the IC work piece, and focusing the writing laser on the Integrated Circuit work piece to write or etch Integrated Circuit patterns on the work piece.
Various methods have been developed in the prior art for automatic distance measurement and for automatic focusing of cameras and laser beams. However, the present invention represents a major innovation that is not anticipated in the prior art.
A particular advantage of the present invention is that it works equally well on a work piece that has a non-reflective pattern on it, and on a work piece that has a completely reflective mirror surface prior to processing. Previous systems for focusing lasers to etch patterns on Integrated Circuit chips have found it difficult to use optical techniques to determine the distance to, and to focus light on, a mirror surface. This invention is an advance since traditional optical distance measurement and focusing systems find it impossible to measure to and focus on a mirror reflective surface. Instead, prior art responds only to the virtual image reflected in the mirror surface. This invention is of great utility since integrated circuit chips and wafers are manufactured from a perfect mirror surface, prior to their etching to establish the circuit pattern on them.
Furthermore, this invention allows for optical focusing, distance measurement and laser etching, with the same laser and the same optical system applied to all three functions. Previous machinery that used other optical techniques for distance measurement and laser focusing, and used lasers for etching integrated circuit chips, required two different lasers for the functions (that is, a laser for the functions of distance measurement and focusing, and a laser for the function of laser etching). This raised factors of additional cost and calibration problems between the measurement/focusing lasers and the etching lasers. This is overcome with the present invention that can both focus and etch with one laser and optical system.